ci: lint the Go 1.27 job on go1.27.1 until golangci-lint reads 1.27.2 export data

[chrisnojima]

What

CI on master fails every night in the 1.27.x golangci-lint step, with typecheck errors like export data version 5 is greater than maximum supported version 4. setup-go now resolves 1.27.x to Go 1.27.2. That release writes export data version 5, and golangci-lint's bundled golang.org/x/tools reads only up to version 4. The other jobs show as failed only because fail-fast cancels them.

This sets GOTOOLCHAIN=go1.27.1 on the golangci-lint step, for the 1.27.x job only. Build, govulncheck and tests still run on the latest 1.27, and the 1.26.x job is unchanged.

• Bumping golangci-lint doesn't help: v2.14.0 fails the same way.
• Building golangci-lint with go1.27.2 doesn't help either: the version-4 limit is in its x/tools.
• Remove the override once a golangci-lint release can read version 5.

Testing

Locally, with go1.27.2 as the installed Go:

golangci-lint	Toolchain	Result
prebuilt v2.13.2	go1.27.2	3 typecheck errors, same as CI
prebuilt v2.14.0	go1.27.2	the same 3 errors
v2.13.2 built with go1.27.2	go1.27.2	the same 3 errors
prebuilt v2.13.2	GOTOOLCHAIN=go1.27.1	0 issues